1. The study of the influence of an electric field on optical phenomena, as in the electro-optical Kerr effect (pattern of double refraction) and the Stark effect (effect of an electric field on spectrum lines).
2. A branch of physics that functions with the influence and effects of an electric field on light going through the optical properties of matter; especially, in its crystalline form.

These properties include the transmission, emission, and the absorption of light.

The term electro-optics is used interchangeably with the broader term optoelectronics.